This disclosure relates to detecting the existence of a sleep disorder in an individual using heart activity.
A sleep disorder is any of a group of syndromes characterized by disturbance in an individual's sleep, including, e.g., the amount of sleep, the quality or timing of sleep, or in behaviors or physiological conditions associated with sleep.
One class of sleep disorder is sleep apnea, which refers to sleep disorders that are characterized by pauses in breathing during sleep. Clinically significant sleep apnea can be associated with five or more pauses (i.e., five or more “apnea”) per hour, with each individual pause lasting longer than 10 seconds. Sleep apnea can be associated with other physiological indicators, such as neurological arousals, blood oxygen desaturation, or combinations thereof.
One class of sleep apnea is obstructive sleep apnea (OSA). Obstructive sleep apnea is caused by physical obstruction of the airway that interrupts breathing despite an individual's effort to breathe. For example, in some forms of obstructive sleep apnea, soft tissue of the airway collapses to obstruct breathing as muscle tone relaxes during sleep.
Another class of sleep apnea is central sleep apnea. In contrast with obstructive sleep apnea, central sleep apnea is caused by a disorder of the central nervous system. For example, the nerve signals that trigger breathing can be delayed and an individual to miss one or more breathing cycles. If the pause in breathing is long enough, blood oxygen can drop and carbon dioxide can increase. In some instances, these conditions can trigger additional physiological effects, including nerve cell necrosis.
Another class of sleep disorder is Cheyne-Stokes respiration. In individuals suffering from Cheyne-Stokes respiration, breathing during sleep alternates between rapid and absent. Cheyne-Stokes respiration can be associated with heart failure, strokes, traumatic brain injuries, and brain tumors. In some instances, it can also occur during sleep at high altitudes, or as a result of toxic metabolic encephalopathy or carbon monoxide poisoning.
Another class of sleep disorder is periodic limb movement disorder, which is also referred to nocturnal myoclonus. In individuals suffering from periodic limb movement disorder, limbs are moved involuntarily during sleep to such an extent that the individual's sleep is disturbed. The movements, which occur in the legs more commonly than in the arms, generally occur for between 0.5 and 5 seconds and recur at intervals of between 5 and 90 seconds.
Polysomnography is a multi-parametric test that can be used to detect sleep apnea and other sleep disorders. During a typical polysomnography test, a variety of different aspects of the physiological condition of an individual are monitored. For example, the electrical activity of the brain (EEG), electrical activity associated with eye movements (EOG), electrical activity associated with other muscular activity or movements (EMG), the electrical activity of the heart (ECG), blood oxygen saturation (using, e.g., pulse oximetry), and movement of various parts of the body (e.g., the chest wall, the upper abdominal wall, the nose and nostrils, the chin, and/or the legs) can be monitored during polysomnography tests. Moreover, patients can be monitored visually by medical personnel during polysomnography tests.